This invention relates generally to an electrical connector for printed circuit boards, and more particularly to an electrical connector wherein a low or zero insertion force is applied to the circuit board when the circuit board is inserted into the connector.
Low insertion force or zero force connectors are well known and come in a variety of configurations. Many electrical circuits are printed, or otherwise formed on either or both surfaces of an insulating substrate. The boards or substrates are inserted into receptacles which are then interconnected into other circuit devices to form complex electronic devices. The board has a plurality of conductive pads or strips on the marginal portions thereof which make contact to a "chip" or circuit in the center portion thereof.
The connector includes contacts for engaging the strips of conductive material on the board and making electrical connection with external circuit. The external circuit may be in the form of a board having a plurality of openings therein with each opening coated with an electrically conductive material. To complete the electrical connection with the printed boards, the board is inserted edgewise into a receiving zone to mechanically and electrically engage the contact points.
Since it is necessary to have many contact points for engaging the multiple strips on the board, the force required to insert the board into the receptacles can be high even though the individual force exerted by one contact is low.
Also, insertion of a board into the connector tends to wear away the terminal strips on the board and deteriorate the contacts. This may be detrimental to both the electrical and mechanical integrity of the system and this tends to reduce the useful life of the connector and the board. Thus, reduction of the force applied by the individual contacts against the circuit board permits the use of a greater number of contacts for a given insertion force.
An example of one type of known low insertion force connector can be found in U.S. Pat. No. 3,899,234 to Yeager et al. An elongated contact drive member is positioned at the bottom of an aperture and the cam is arranged to move therein. The connector is arranged for cam movement to drive the contacts into engagement with the board or drive the cams into and out of engagement position.
U.S. Pat. No. 3,478,301 to Conrad et al. utilizes a system where insertion of a printed circuit board into the receptacle actuates cam members to displace the contact members to electrical engagement with the circuit board. U.S. Pat. No. 4,021,091 to Anhalt et al. describes a connector having a hollow shell mounted over the contacts which is vertically movable within a housing. An elongated cam rod inside the outer housing is longitudinally movable to shift the shell downwardly to cam actuate the contacts.
U.S. Pat. No. 3,997,231 to Sherwood describes a connector having a camming device comprising a matched pair of blocks which urge the contacts into a circuit board engaging position when they are moved upwardly.
U.S. Pat. No. 4,179,177 to Lapraik relates to a connector or inner housing having upright sections which urge board portions of contacts apart as a cam is actuated.
U.S. Pat. No. 4,303,294 to Hamsher, Jr. et al. relates to connector having a cam which actuates an upright section to provide deflection of a compound beam contact. The contacts exert a force on the upright section to return it to a lower position. Other and further objects of the present invention will become apparent from the following description.
In accordance with the present invention, there is provided a zero or low insertion force connector for making electrical connection between a circuit board and an external circuit comprising an elongated outer housing having a channel extending in the longitudinal direction, a plurality of contacts mounted on said outer housing on either side of said channel, said contacts having lower end portions projecting exteriorly of said outer housing through the bottom of said channel, and upper portions interior said outer housing adapted to contact opposite sides of a circuit board, an inner housing mounted interior said outer housing for movement inwardly and outwardly along a vertical direction normal to the longitudinal direction, an ovally shaped cam having an axis of rotation extending in the longitudinal direction, said cam being adapted to be rotated from a first position presenting a narrow cross section in the vertical direction to a second position presenting a wider cross section in the vertical direction, a pair of first cam engaging surfaces and a pair of second cam engaging surfaces, said inner and outer housings each including respective first and second cam engaging surfaces, said first surfaces being diametrically opposed along the vertical direction and adapted to be moved apart when said cam is rotated from said first position, said second surfaces being laterally displaced from said first surfaces along the direction of rotation of said cam and adapted to be moved apart when said cam is rotated from said second position, said inner housing including means adapted to engage and urge upper portions of said contacts apart when said cam is rotated from one of said positions to the other of said positions whereby removal or insertion of a circuit board is permitted.